Golf balls are made in a variety of constructions and compositions. Generally, a core is surrounded by a cover, with at least one intermediate layer optionally disposed there between. Golf ball manufacturers continuously experiment with constructions and material formulations in order to target and improve aerodynamic and/or inertial properties and achieve desired feel without sacrificing durability.
Examples of golf ball materials range from balata to polybutadiene, ionomer resins, polyurethanes, and/or polyureas. Typically, outer layers are formed about the spherical outer surface of an inner golf ball component via compression molding, casting, or injection molding.
A known problem with golf balls is that water vapor sometimes penetrates into golf ball materials, which can harmfully affect golf ball properties. For example, when a polybutadiene core cross-linked with peroxide and/or zinc diacrylate absorbs water, the core tends to lose resiliency, and the compression and coefficient of restitution (COR) of the ball may change.
The industry has addressed this problem by applying a moisture barrier layer over a golf ball material that would otherwise be vulnerable to water penetration. In this regard, an effective moisture barrier layer has a water vapor transmission rate that is low enough to create a barrier against moisture penetration into the enveloped material and thereby protect the material against the negative effects of water.
Additionally, a moisture barrier layer is ideally as thin as possible in order to maximize its effectiveness in resisting moisture without compromising golf ball properties such as COR, durability, and compression or unnecessarily increasing the cost of materials and processing.
Some prior thin moisture barrier layers involve nano-composite filled elastomeric coatings containing exfoliated platelet particles or a specialized low transmission polymer such as polyvinylidene chloride. However, these materials are known to display inter-layer adhesion problems, durability issues, and resilience deficiency. In fact, loss of barrier effectiveness sometimes occurs when the moisture barrier layer cracks upon the golf ball's impact with a club. Meanwhile, golf balls incorporating non-ionomeric polyolefin materials in thin moisture barrier layers of about 0.010 inches or less are also disclosed. See, e.g., U.S. Pat. No. 8,303,436 of Sullivan et al.
However, ionomeric materials are often preferred in many constructions due to their superior durability and desirable performance characteristics such as scuff resistance and rebound. Also being known to be non-soluble in water, ionomers would therefore serve as excellent moisture vapor barrier materials. But golf ball manufacturers have encountered difficulties in applying ionomeric materials in desirably thin layers. In this regard, ionomers generally require high pressures and temperatures to form a layer via typical processes like RPIM or compression molding, thereby making layers under 0.030 inches difficult to mold unless included in blends with non-ionomeric compositions such as polyvinyl alcohol copolymer and polyamides.
Accordingly, there is a need for golf balls incorporating thin ionomeric moisture vapor barrier layers of about 0.010 inches or less without using the solvents, pressure vessels or intensive mechanical agitation necessary to incorporate ionomers into golf ball layers having conventional thicknesses. Such a golf ball would permit golf ball manufacturers to cost effectively capitalize on the superior hydrophobic qualities of ionomers, which already have a great track record for durability and performance. The present invention provides golf balls and methods that address and solve this need.